Grinding chips which occur in the machining of an iron-based metal such as bearing steel, carburized steel and the like (hereinafter, the term “machining” will be used to represent a concept also including grinding, super-finishing grinding, lapping and the like) are recovered in the form of cotton-like (fibrous) aggregates including a grinding fluid containing water and oil, abrasive grains, and the like. Since the cotton-like aggregates contain a considerable quantity of pure iron, there have been made attempts to reuse the aggregates as steelmaking material. Unfortunately, however, the cotton-like aggregates contain such a large quantity of water as to cause bumping (phreatic explosion) if the aggregates are directly charged into a blast furnace. It may be contemplated to remove the water from the cotton-like aggregates by centrifugation or the like. In this case, however, the oil contained in the cotton-like aggregates is also removed along with the water and hence, the pure iron as a component of the grinding chips is converted to iron oxide due to the self heating of the cotton-like aggregates. Therefore, the resultant aggregates need be reduced so as to be reused as steelmaking material. The use of a reducing agent results in increased costs.
On the other hand, the grinding chips with the oil adhered thereto are less prone to adhere to each other. In the case of cotton-like aggregates containing a large quantity of grinding chips from an iron-based metal containing not less than 0.2 wt % of carbon, great springback is encountered when the aggregates are compression molded. Hence, the compression molding of the cotton-like aggregates involves difficulty about accomplishing solidification to a desired strength. Accordingly, if such compacted cotton-like aggregates are charged into the blast furnace, the aggregates are scatteringly carried upward so that most of them is collected by a dust collector.
In addition, the fibrous grinding chips contained in the cotton-like aggregates are hard to crush by means of a hammer mill or the like and hence, the cotton-like aggregates cannot be sheared finely. This leads to a difficulty of processing the cotton-like aggregates into briquettes or the like.
In reality, therefore, the cotton-like aggregates are not put to reuse but committed to a waste processing contractor for landfill disposal.
In a steel making process including a smelting step and the like, on the other hand, there occur dusts bearing iron and heavy metals. Hence, it is a general practice to collect such dusts as recovery dusts (OG dusts) (see, for example, Unexamined Japanese Patent Publication No.7 (1995)-97638). Unfortunately, if such recovery dusts are directly charged into the blast furnace, the dusts are scatteringly carried upward to be collected by the dust collector again. As a result, the dusts are not put to reuse but committed to the landfill disposal.
However, the landfill disposal is undesirable from the standpoint of the effective utilization of resources. Furthermore, the landfill disposal entails the environmental deterioration as well as the increase of the disposal costs. The recovery dusts, in particular, requires an even greater disposal cost because the dusts contain heavy metals and must be committed to the landfill disposal as special industrial wastes.
It is an object of the invention to provide a brittle compact and iron-based powder material providing an effective reuse of grinding chips, as well as a method for producing the same.
It is another object of the invention to provide an iron-based powder material providing an effective reuse of the grinding chips together with the recovery dusts, as well as a method for producing the same.